Dual-image optoelectronic imaging apparatus including birefringent prism arrangement

Abstract

A birefringent prism (36) is disposed in front of the entrance aperture (26a) of a Cassegrain-type telescope (26) which constitutes the optical focussing assembly in a tracking system for a guided missile (10) or the like. The prism (36) refracts first radiation (O) having a first polarization in a first direction, and refracts second radiation (E) having a second polarization which is orthogonal to the first polarization in a second direction which is deviated from the first direction by a predetermined angle Δφ. The telescope (26) focusses the first and second radiation (O,E) to form separate, laterally displaced first and second optical images (46,50) on first and second respective sections (34a,34b) of a focal plane photodetector array (34). Polarizing filters (56,58) which pass only the first and second polarizations therethrough are disposed in front of the respective sections (34a,34b) of the photodetector array (34) to eliminate optical crosstalk between the two images (46,50). Optical bandpass filters (54,52) having different wavelength passbands may also be provided in front of the two sections (34a,34b) of the photodetector array (34) such that the two images (46,50) constitute different color images of the scene (16).

I claim: 
     
       1. An optical imaging apparatus for producing first and second optical images of a scene including first and second electromagnetic radiation having first and second orthogonal polarizations respectively received from the scene, comprising: a birefringent prism which refracts the first radiation therethrough in a first direction and refracts the second radiation therethrough in a second direction which is deviated from the first direction by a predetermined angle; and   optical means for focussing the first and second radiation at a focal plane to produce the first and second optical images respectively;   said predetermined angle being selected such that the first and second optical images are laterally displaced from each other by a predetermined distance in the focal plane.   
     
     
       2. An imaging apparatus as in claim 1, in which: the first and second radiation are incident on the prism along a first axis;   the prism has a triangular cross-section in a plane defined by the first axis and a second axis which perpendicularly intersects the first axis, the prism extending perpendicular to said plane; and   the prism has an ordinary axis which is parallel to the first axis, and an extraordinary axis which is perpendicular to the first axis.   
     
     
       3. An imaging apparatus as in claim 2, in which the ordinary axis of the prism is parallel to the second axis. 
     
     
       4. An imaging apparatus as in claim 2, in which the prism has a right triangular cross-section in said plane. 
     
     
       5. An imaging apparatus as in claim 2, in which the prism has an isosceles triangular cross-section in said plane. 
     
     
       6. An imaging apparatus as in claim 2, further comprising a second birefringent prism disposed adjacent to said prism, the second prism having an ordinary axis which is parallel to the first axis and an extraordinary axis which is perpendicular to the first axis. 
     
     
       7. An imaging apparatus as in claim 6, in which the extraordinary axis of the second prism is parallel to the ordinary axis of the first prism. 
     
     
       8. An imaging apparatus as in claim 6, in which the second prism has a triangular cross-section in said plane which is conjugate to said cross-section of said prism, and extends perpendicular to said plane. 
     
     
       9. An imaging apparatus as in claim 8, in which: said prism has a right triangular cross-section including a perpendicular face which faces the scene and an inclined face which faces the focal plane; and   the second prism has a right triangular cross-section which is inverted relative to said prism, including a perpendicular face which faces the focal plane and an inclined face which faces the scene and mates with the inclined face of said prism.   
     
     
       10. An imaging apparatus as in claim 1, further comprising optoelectronic sensor means disposed in the focal plane for producing electrical signals corresponding to the first and second optical images. 
     
     
       11. An imaging apparatus as in claim 10, in which the sensor means comprises an optoelectronic focal plane photodetector array. 
     
     
       12. An imaging apparatus as in claim 10, in which: the sensor means has a first section on which the first optical image is incident and a second section on which the second optical image is incident; and   the imaging apparatus further comprises:   first polarizing means disposed between the optical means and the first section of the sensor means for transmitting the first radiation having the first polarization therethrough and blocking the second radiation having the second polarization; and   second polarizing means disposed between the optical means and the second section of the sensor means for transmitting the second radiation having the second polarization therethrough and blocking the first radiation having the first polarization.   
     
     
       13. An imaging apparatus as in claim 12, further comprising: first optical filter means disposed between the optical means and the first section of the sensor means for transmitting only a first optical wavelength band therethrough; and   second optical filter means disposed between the optical means and the second section of the sensor means for transmitting only a second optical wavelength band therethrough which is different from the first optical wavelength band.   
     
     
       14. An imaging apparatus as in claim 1, in which the optical means is disposed between the prism and the focal plane. 
     
     
       15. An imaging apparatus as in claim 14, in which: the optical means has an entrance aperture; and   the prism is disposed closely adjacent to the entrance aperture.   
     
     
       16. An imaging apparatus as in claim 15, in which the optical means comprises a Cassegrain-type telescope. 
     
     
       17. An imaging apparatus as in claim 1, in which the prism is disposed in a collimated image area of the optical means. 
     
     
       18. An imaging apparatus as in claim 1, in which: the optical means has a predetermined angular field-of-view; and   said predetermined angle is approximately one-half said field-of-view.   
     
     
       19. In a guided missile, a tracking system including an optical imaging apparatus for producing first and second optical images of a scene including first and second electromagnetic radiation having first and second orthogonal polarizations respectively received from the target, comprising: a birefringent prism which refracts the first radiation therethrough in a first direction and refracts the second radiation therethrough in a second direction which is deviated from the first direction by a predetermined angle; and   optical means for focussing the first and second radiation at a focal plane to produce the first and second optical images respectively;   said predetermined angle being selected such that the first and second optical images are laterally displaced from each other by a predetermined distance in the focal plane.   
     
     
       20. A guided missile as in claim 19, in which: the first and second radiation are incident on the prism along a first axis;   the prism has a triangular cross-section in a plane defined by the first axis and a second axis which perpendicularly intersects the first axis, the prism extending perpendicular to said plane; and   the prism has an ordinary axis which is parallel to the first axis, and an extraordinary axis which is perpendicular to the first axis.   
     
     
       21. A guided missile as in claim 20, in which the ordinary axis of the prism is parallel to the second axis. 
     
     
       22. A guided missile as in claim 20, in which the prism has a right triangular cross-section in said plane. 
     
     
       23. A guided missile as in claim 20, in which the prism has an isosceles triangular cross-section in said plane. 
     
     
       24. A guided missile as in claim 20, further comprising a second birefringent prism disposed adjacent to said prism, the second prism having an ordinary axis which is parallel to the first axis and an extraordinary axis which is perpendicular to the first axis. 
     
     
       25. A guided missile as in claim 24, in which the extraordinary axis of the second prism is parallel to the ordinary axis of the first prism. 
     
     
       26. A guided missile as in claim 24, in which the second prism has a triangular cross-section in said plane which is conjugate to said cross-section of said prism, and extends perpendicular to said plane. 
     
     
       27. A guided missile as in claim 26, in which: said prism has a right triangular cross-section including a perpendicular face which faces the target and an inclined face which faces the focal plane; and   the second prism has a right triangular cross-section which is inverted relative to said prism, including a perpendicular face which faces the focal plane and an inclined face which faces the target and mates with the inclined face of said prism.   
     
     
       28. A guided missile as in claim 19, further comprising optoelectronic sensor means disposed in the focal plane for producing electrical signals corresponding to the first and second optical images. 
     
     
       29. A guided missile as in claim 28, in which the sensor means comprises an optoelectronic focal plane photodetector array. 
     
     
       30. A guided missile as in claim 28, in which: the sensor means has a first section on which the first optical image is incident and a second section on which the second optical image is incident; and   the imaging apparatus further comprises:   first polarizing means disposed between the optical means and the first section of the sensor means for transmitting the first radiation having the first polarization therethrough and blocking the second radiation having the second polarization; and   second polarizing means disposed between the optical means and the second section of the sensor means for transmitting the second radiation having the second polarization therethrough and blocking the first radiation having the first polarization.   
     
     
       31. A guided missile as in claim 30, further comprising: first optical filter means disposed between the optical means and the first section of the sensor means for transmitting only a first optical wavelength band therethrough; and   second optical filter means disposed between the optical means and the second section of the sensor means for transmitting only a second optical wavelength band therethrough which is different from the first optical wavelength band.   
     
     
       32. A guided missile as in claim 19, in which the optical means is disposed between the prism and the focal plane. 
     
     
       33. A guided missile as in claim 32, in which: the optical means has an entrance aperture; and   the prism is disposed closely adjacent to the entrance aperture.   
     
     
       34. A guided missile as in claim 33, in which the optical means comprises a Cassegrain-type telescope. 
     
     
       35. A guided missile as in claim 19, in which the prism is disposed in a collimated image area of the optical means. 
     
     
       36. A guided missile as in claim 19, in which: the optical means has a predetermined angular field-of-view; and   said predetermined angle is approximately one-half said field-of-view.